1. Field of the Invention
The present invention relates to a system for checking an electrically conductive pattern such as an antenna pattern on a sheet of window glass.
2. Description of the Relevant Art
FIG. 9 of the accompanying drawings shows a conventional conductivity inspecting system comprising a continuity checker 101 for checking an antenna pattern 103 on a sheet 102 of window glass for a wire break. The continuity checker 101 operates as follows: As shown in FIG. 9, the continuity checker 101 has a probe 104 positioned in contact with a terminal 100 of the antenna pattern 103. While the probe 104 is being held in contact with the terminal 100, another probe 105 of the continuity checker 101 is successively brought into contact with tip ends P1, P2, P3, P4, P5, P6 of branch arms of the antenna pattern 103 to check the entire antenna pattern 103 for a wire break. The continuity checker 101 has an electric circuit (not shown) which includes a buzzer for producing an audible sound when the resistance of an antenna pattern portion measured between the probes 104, 105 is below a predetermined value.
Another conventional conductivity inspecting system is shown in FIG. 10 of the accompanying drawings. The conductivity inspection system shown in FIG. 10 comprises a Q-meter 111 to check an antenna pattern 113 which is formed between superposed layers of a sheet 112 of laminated glass. The Q-meter 111 is used because a usual continuity checker, as shown in FIG. 9, cannot be used with the antenna pattern 113 as it is not exposed but embedded in the laminated glass 112.
In operation, while a probe 114 of the Q-meter 111 is being held in contact with a terminal 115 of the antenna pattern 113, a frequency adjusting knob 117 of the Q-meter is turned to maximize or minimize the movement of a pointer 116 of the Q-meter for thereby achieving a resonant condition. Thereafter, an operator's fingertip is brought into touch with the surface of the laminated glass 112 at a tip end 118 of the antenna pattern 113.
If the antenna pattern 113 has no wire break, then a capacitor is coupled to the tip end 118 by the operator's fingertip, resulting in a shift in the resonant frequency. Accordingly, the pointer 116 shifts from a resonant position which it has achieved previously. If the antenna pattern 113 has suffered a wire break, then the pointer 116 does not move. Therefore, if pointer 116 moves, the antenna pattern 113 is acceptable; if pointer 116 does not move, the antenna pattern 113 is unacceptable.
The continuity checker as shown in FIG. 9 is disadvantageous in that it takes a relatively long period of time to check an antenna pattern especially if the pattern has many branch arms.
The conductivity inspection system using a Q meter as shown in FIG. 10 requires a tedious and time-consuming process to achieve a resonant condition.
Another problem is that any of the conventional conductivity inspection systems fails to detect pattern short circuits other than wire breaks.